1. Field of the Invention
The present invention relates to a magnetoresistive effect element which detects magnetism by passing a sense current in a direction perpendicular to a surface of a magnetoresistive effect film, and a manufacturing method thereof.
2. Description of the Related Art
The performance of magnetic devices, especially magnetic heads is dramatically enhanced by using a giant magneto-resistive effect (Giant Magneto-Resistive Effect: GMR). Application of a spin-valve film (Spin-Valve: SV film) to a magnetic head, a MRAM (Magnetic Random Access Memory) and the like has brought about great technological advance to the magnetic device field.
“Spin-valve film” is a stacked film having a structure in which a nonmagnetic spacer layer is sandwiched between two ferromagnetic layers, and is also called a spin-dependent scattering unit. Magnetization of one of the two ferromagnetic layers (called “a pinned layer”, “fixed magnetization layer” and the like) is fixed with an antiferromagnetic layer or the like, and magnetization of the other layer (called “a free layer”, “free magnetization layer” and the like) is rotatable in accordance with an external magnetic field. In the spin-valve film, a relative angle of the magnetization directions of the pinned layer and the free layer changes, and thereby, giant magneto-resistive change is obtained.
Magnetoresistive effect elements using spin-valve films include a CIP (Current In Plane)-GMR element, a CPP (Current Perpendicular to Plane)-GMR element, and a TMR (Tunneling Magneto Resistance) element. In the CIP-GMR element, a sense current is passed parallel with the surface of the spin-valve film, and in the CPP-GMR and TMR elements, a sense current is passed in a direction substantially perpendicular to the planes of the spin-valve film. The method of passing a sense current perpendicularly to the film plane attracts more attention as the technique adaptable to a high recording density head of the future.
Here, in a metal CPP-GMR element with a spin-valve film formed of a metal layer, the resistance change amount by magnetization is small, and it is difficult to detect a weak magnetic field (for example, the magnetic field in the magnetic disk of high recording density).
As a spacer layer, a CPP element using an oxide layer [NOL (nano-oxide layer)] including a current path in the thickness direction is proposed (see JP-A 2002-208744 (KOKAI)). In this element, both the element resistance and MR ratio can be increased by the current-confined-path [CCP (Current-confined-path)] effect. Hereinafter, the element will be called a CCP-CPP element.
Presently, magnetic storage devices such as an HDD (Hard Disk Drive) are used for personal computers, portable music players and the like. However, if the use purpose of the magnetic storage device is further increased and high density storage advances in the future, demand for reliability becomes more stringent. For example, it becomes necessary to enhance reliability under the condition at a higher temperature and under the operating environment at a higher speed. For this purpose, it is desirable to enhance reliability of the magnetic heads more than before.
A CCP-CPP element is especially low in resistance as compared with the conventional TMR element, and therefore, it is applicable to a high-end magnetic storage device for use in a server/enterprise requiring a higher transfer rate. For such a high-end use, high areal density and high reliability are required to be satisfied at the same time. For these use purposes, it is desirable to enhance reliability at a higher temperature. Namely, it becomes necessary to use a CCP-CPP element under a severer environment (high-temperature environment or the like), under more strict use conditions (read of information in a magnetic disk rotating at a high speed, and the like).
The present invention has an object to provide a magnetoresistive effect element which is applicable to a magnetic storage device of high density storage, and is enhanced in reliability, and a manufacturing method thereof.